Amazon has been offering discounts for holders of EBT cards since June. EBT stands for Electronic Benefit Transfer, and these debit cards are the primary way that recipients of SNAP — otherwise known as food stamps — get their benefits. Amazon has now started offering the discount to Medicaid recipients as well.

The discount is substantial: Amazon asks these lower-income customers to pay $6 a month.

The cheapest option for a typical Amazon Prime member is to pay $100 a year to renew their membership on an annual basis. That translates to about $8 a month.

All recipients of either EBT or Medicaid benefits need to do is show their card and verify their status with Amazon by taking a picture. They can then sign up for Prime as usual.

Most of these potential customers are younger or have a lower income than Amazon's traditionally well-heeled Prime members. But they spend money, too, and as Amazon dives more heavily into its fresh grocery and essentials business, the convenience may drive them there instead.

The low-income customer segment has long been Walmart's forte, and the retailer has its own products geared toward them, like low-fee checking accounts and money services that can be done in-store.